Telemetric medical system and method

ABSTRACT

A telemetric medical system comprises a telemetric medical sensor for implantation in a patient&#39;s body for measuring a parameter therein. The sensor comprises a housing and a membrane at one end of the housing. The membrane is deformable in response to the parameter. A microchip is positioned within the housing and operatively communicates with the membrane for transmitting a signal indicative of the parameter. The system also includes a signal reading and charging device locatable outside of a patient&#39;s body for communication with the sensor. The signal reading and charging device comprises a casing and a circuit within the casing. The circuit includes a logic control unit and a processing unit. The logic control unit sends a powering signal to the sensor for remotely powering the sensor. The logic control unit also receives the transmitted signal from the sensor wherein the processing unit operatively connected to the control unit converts the transmitted signal by the sensor into a measured parameter.

FIELD OF THE INVENTION

The present invention relates, in general, to telemetric medicaldevices. More particularly, the present invention relates to a noveltelemetric medical system which is capable of various medicalapplications including the measurement of a parameter within a patient'sbody, particularly an organ. One such application of the presentinvention is as an implantable telemetric endocardial pressure system,its associated novel components and their novel methods of use.

BACKGROUND OF THE INVENTION

In general, the use of implantable medical sensors in a patient isknown. One example for an implantable sensor is disclosed in U.S. Pat.No. 4,815,469 (Cohen et al.) incorporated herein by reference. Thedisclosure is directed to an implantable medical sensor which determinesthe oxygen content of blood. The sensor includes a miniaturized hybridcircuit that includes light-emitting diode means, phototransistor means,and a substrate to which the light-emitting diode means andphototransistor means are bonded in a desired circuit configuration. Thehybrid circuit is hermetically sealed within a cylindrical body madefrom a material that is substantially transparent to light, such asglass. Feedthrough terminals provide means for making an electricalconnection with the hybrid circuit. The light-emitting diode means isdriven with a stair-stepped current pulse. The purpose of the sensor isto sense the reflective properties of body fluid, such as blood, forspectrophotometric analysis. In one embodiment, the sensor is embeddedwithin a bilumen pacemaker lead and positioned near the distal electrodeof the lead so that the sensor resides within the heart when the lead isimplanted within a patient, thereby allowing the sensed oxygen contentof the blood within the heart to be a physiological parameter that canbe used to control the pacing interval of a rate-responsive pacemaker.

U.S. Pat. No. 5,353,800 (Pahndorf et al.) discloses an implantablepressure sensor lead having a hollow needle adapted to be screwed into apatient's heart. The pressure sensor is supplied electrical powerthrough conductors in the sensor.

There are cases where permanent positioning of the sensor is needed. Onesuch case, for example, is disclosed in U.S. Pat. No. 5,404,877 (Nolanet al.), which is incorporated herein by reference. A leadlessimplantable cardiac arrhythmia alarm is disclosed which continuouslyassesses a patient's heart function to discriminate between normal andabnormal heart functioning and, upon detecting an abnormal condition,generates a patient-warning signal. The alarm is capable of sensingimpedance measurements of heart, respiratory and patient motion and,from these measurements, generating an alarm signal when themeasurements indicate the occurrence of a cardiac arrhythmia. It isimportant to note that the sensor uses an antenna system having a coilinductor for generating an electromagnetic field into tissue fordetecting changes in impedance which relate to a physiologicalphenomena. For example, the size of the inductor is preselected in orderto match the dimensions of the organ or structure to be measured.

There are also several known implantable devices that employ telemetryfor transmitting or receiving data from an external device. One suchdevice is, for example, the system disclosed in U.S. Pat. No. 6,021,352(Christopherson et al.). The device utilizes a pressure sensor as atransducer for sensing respiratory effort of the patient. Respiratorywaveform information is received by an implantable pulse generator(IPG)/simulator from a transducer and inspiration synchronous simulationis provided by the IPG.

One other telemetric implantable device is disclosed in U.S. Pat. No.5,999,857 (Weijand et al.). This reference discloses a telemetry systemfor use with implantable devices such as cardiac pacemakers and thelike, for two-way telemetry between the implanted device and an externalprogrammer. The system employs oscillators with encoding circuits forsynchronous transmission of data symbols in which the symbols form thetelemetry carrier. The system provides circuits for higher density dataencoding of sinusoidal symbols, including combinations of BPSK, FSK, andASK encoding. Embodiments of transmitters for both the implanted deviceand the external programmer, as well as modulator and demodulatorcircuits, are also disclosed. It is important to note that the implantdevice has its own power supply in the form of a battery for poweringall of the circuitry and components of the implanted device.

It is also important to note, that to date, there has not been anytelemetric medical system that is both a highly efficient system due toits components and their ease of use while providing extremely accurateinformation regarding a measured parameter in a patient's body.

SUMMARY OF THE INVENTION

The present invention is directed to a novel telemetric medical systemfor use with various medical applications such as monitoring medicalconditions or measuring parameters within a patient's body for differenttypes of organs, including tissue, as well as their function.

The present invention is a telemetric medical system comprising atelemetric medical sensor for implantation in a patient's body formeasuring a parameter therein. The sensor comprises a housing, and amembrane at one end of the housing, wherein the membrane is deformablein response to the parameter. A microprocessor, which is in the form ofa microchip, is positioned within the housing and operativelycommunicates with the membrane for transmitting a signal indicative ofthe parameter.

A signal reading and charging device is locatable outside of a patient'sbody and communicates with the sensor. The signal reading and chargingdevice comprises a casing and a circuit within the casing. The circuitcomprises a logic control unit and a processing unit operativelyconnected to the logic control unit. The logic control unit, through adeep detector, receives the transmitted signal from the sensor. Thelogic control unit also sends a powering signal to the sensor through asine wave driver for remotely powering the sensor. The powering signalis a sinusoidal wave signal approximately 4-6 MHz. The processing unitincludes an algorithm for converting the transmitted signal receivedfrom the sensor into a measured parameter. Additionally, the signalreading and charging device includes a power source operativelyconnected to the circuit and a power switch for activating anddeactivating the device.

The signal reading and charging device also includes an antenna coil forsending the powering signal to the sensor and for receiving thetransmitted digital signal from the sensor. The antenna coil hasinductive coupling with the sensor. The signal reading and chargingdevice also includes a display, which is an LCD screen, for displayingthe measured parameter.

The microprocessor, which is in the form of a microchip, comprises anarray of photoelectric cells which are arranged in staggered rows. Thearray also includes a reference photoelectric cell located at one end ofthe array. A light emitting diode (LED) transmits light at thephotoelectric cells and the reference photoelectric cell.

The sensor further comprises a shutter connected to the membrane andmoveable between the photoelectric cells and the LED in response to thedeforming of the membrane. The sensor is arranged such that thereference photoelectric cell is not blocked by the shutter and remainsexposed to the light emitted by the LED.

The microchip further comprises a plurality of comparators operativelyconnected to the photoelectric cells and a buffer operatively connectedto the comparators for storing and transmitting the digital signal. Thesensor further comprises an antenna, in the form of a coil, operativelyconnected to the microchip wherein the antenna is located at theexterior of the housing. Alternatively, the antenna is located withinthe housing of the sensor. Preferably, the antenna coil is made of wirecomprising silver and platinum iridium. Additionally, the antenna has20-25 turns.

The sensor according to the present invention further comprises aplurality of anchoring legs resiliently attached to the housing foranchoring the sensor into tissue. Additionally, the housing optionallyincludes a notch in an outer surface of the housing to facilitatedeployment. The housing further optionally includes a circumferentialgroove at the notch to further facilitate deployment.

In another embodiment for the sensor, the housing further includes atapered end and a piercing tip thereon. The tapered end further includeshelical threads thereon for threading the sensor housing directly intotissue. An alternative embodiment includes a plurality of tissue barbson the tapered end for anchoring the sensor housing directly intotissue.

The present invention also includes a method for telemetricallymeasuring a parameter in a patient's body comprising the steps ofproviding a telemetric medical sensor comprising a housing having amembrane at one end of the housing wherein the membrane is deformable inresponse to the parameter, and a microchip is positioned within thehousing and operatively communicates with the membrane for transmittinga signal indicative of the parameter. The sensor is implanted at a sitewithin the patient's body and the parameter is telemetrically measuredfrom outside of the patient's body with a signal reading and chargingdevice. The method also includes telemetrically powering the sensor fromoutside of the patient's body with the signal reading and chargingdevice. The measured parameter is then displayed on the display of thesignal reading and charging device.

The method according to the present invention also includes a method fortelemetrically measuring a parameter in a patient's heart wherein themethod comprises the steps of imaging the heart, through the use oftransesophageal ultrasonic imaging, and identifying an implantation sitein the heart. An opening is created in the tissue at the implantationsite and a sensor comprising a housing, a membrane at one end of thehousing wherein the membrane is deformable in response to the parameter,and a microchip positioned within the housing and operativelycommunicating with the membrane for transmitting a signal indicative ofthe parameter is provided. The sensor is placed within the opening andthe parameter is telemetrically measured from outside of the patient'sbody based on the transmitted signal by the sensor.

The method also includes telemetrically powering the sensor from outsideof the patient's body and displaying the measured parameter with asignal reading and charging device. Parameter measurements are mademultiple times per second with the signal reading and charging device.

According to the present invention, the sensor is positioned within achamber of the heart by using the septum as an implantation site, forinstance, the fossa ovalis. Alternatively, the sensor is positionable atother anatomical sites within the heart and other organs and tissue.

One parameter that is measured with the system and method according tothe present invention is hemodynamic blood pressure in a chamber of theheart. Accordingly, the method according to the present inventionfurther includes taking between 10-20 parameter measurements per second.

Moreover, the method further includes creating the opening in the tissuewith a needle. In one embodiment of the present invention, the sensorincludes a plurality of anchoring legs on the sensor for anchoring thesensor to the tissue. Additionally, the sensor is coated with anonthrombogenic agent in order to prevent thrombosis within the heartupon implantation of the sensor.

Another embodiment of the method according to the present inventionincludes a method for telemetrically measuring a parameter in apatient's heart wherein the method comprises the steps of imaging theheart with transesophageal ultrasonic imaging and identifying animplantation site in the heart. A sensor comprising a housing and amembrane at one end of the housing wherein the membrane is deformable inresponse to the parameter and a tapered distal end and piercing tip atthe other end of the housing is provided. The sensor further comprises amicrochip positioned within the housing and operatively communicatingwith the membrane for transmitting a signal indicative of the parameter.The sensor is implanted at the site with the piercing tip and thetapered distal end of the sensor. The parameter is telemetricallymeasured from outside of the patient's body based on the transmissionsignal by the sensor. Additionally, the sensor is telemetrically poweredfrom outside of the patient's body. A signal reading and charging deviceis used outside of the patient's body to measure the parameter, powerthe sensor, and display the measured parameter. Accordingly, parametermeasurements are made multiple times per second with the signal readingand charging device.

The sensor is positioned within a chamber of the heart and theimplantation site is the septum, for instance, at the fossa ovalis. Withthe system and method according to the present invention, one parameterthat is measured is hemodynamic blood pressure within a chamber of theheart. For instance, 10-20 parameter measurements are made per secondfor monitoring blood pressure in accordance with the present invention.

Alternatively, the sensor includes helical threads on the tapered distalend of the sensor and the sensor is anchored into the tissue at the siteby threading the tapered distal end of sensor directly into the tissue.Alternatively, the sensor includes a plurality of tissue barbs on thetapered distal end of the sensor and the sensor is anchored into thetissue at the site with the tissue barbs.

The present invention will be more fully understood from the followingdetailed description of the preferred embodiments thereof, takentogether with the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a telemetric implantable medicalsensor according to the present invention;

FIG. 2 is a top view of the sensor of FIG. 2;

FIG. 3 is a schematic illustration of an alternative embodiment of thesensor of FIG. 1 having a tapered distal end with helical threads andtissue piercing tip for anchoring into tissue;

FIG. 4 is another alternative embodiment of the sensor of FIG. 1 havinga tapered distal end with tissue piercing tip and a plurality of tissuepiercing barbs thereon;

FIG. 5 is a partial perspective view of the sensor of FIG. 1 with someparts removed in order to reveal the internal components of the sensor;

FIG. 6A is schematic diagram illustrating a microprocessor circuit forthe sensor according to the present invention;

FIG. 6B is a schematic diagram illustrating a logic circuit for themicroprocessor circuit of FIG. 6A;

FIG. 7 is a schematic illustration depicting an array of photoelectriccells for the sensor according to the present invention;

FIG. 8 is a schematic illustration depicting the telemetric systemaccording to the present invention including the sensor of FIG. 1 and asignal reading and charging device remotely located from and incommunication with the sensor;

FIG. 9 is a schematic diagram illustrating a read/charge circuit for thesignal reading and charging device of FIG. 8;

FIG. 10 is a schematic illustration of a patient's heart; and

FIG. 11 is a schematic illustration depicting the sensor fully deployedwithin a tissue aperture according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a novel telemetric medical system 30,as schematically illustrated in FIG. 8, as well as its novel componentsand methods of use useful for various medical applications, as explainedand demonstrated herein.

One aspect of the system 30 of the present invention is to remotelysense and measure a characteristic or parameter (or number of variousparameters including the magnitude of any parameter) within a patient'sbody, or within an organ or tissue of the patient's body, through theuse of a novel implantable telemetric medical sensor 50, which iscompletely wireless, and a novel signal reading and charging device 140which operatively communicates with the sensor 50.

Telemetric Sensor

As schematically illustrated in FIG. 1, the sensor 50 comprises ahousing 52 made of a biocompatible material such as polysilicon ortitanium. The housing 52 preferably has a cylindrical shape although anytype of shape for the housing 52 is acceptable. The housing 52 has anapproximate length ranging between 4-5 mm and an approximate diameterranging from 2.5-3 mm in diameter. The housing 52 can also be smaller,e.g. 3 mm in length and a 1-2 mm outer diameter. The housing 52 includescylindrical walls that are approximately 250 μm in thickness. A flexiblemembrane 56 made of a deformable material is fixed to one end of thehousing 52. A notch 58 and a circumferential groove 60 are provided onan exterior surface of the housing 52 for facilitating delivery andimplantation of the sensor 50.

The membrane 56 is made of a flexible or deformable material such aspolysilicon rubber or polyurethane. The membrane 56 has an approximatethickness of 20 μm and has a diameter ranging from approximately 1.5-2mm. The membrane 56 is normally biased outwardly from the housing 52 dueto the interior pressure within the housing 52. The membrane 56 isforced to bulge inwardly into the housing 52 whenever the pressureexterior of the housing 52 exceeds the internal pressure within thehousing 52.

Since the membrane 56 is deformable and normally biased outwardly fromthe housing 52, the membrane 56 responds directly to the environment ofthe tissue or organ being monitored and/or measured for a particularcharacteristic or parameter. In response to even the slightest changesin these characteristics or parameters, the membrane 56 deforms inwardlytoward the interior of the housing 52. Accordingly, there is a directrelationship or correspondence between any change in measuredcharacteristic or parameter and the amount or degree of deforming actionor movement of the membrane 56.

It is important to note that the membrane 56 has a relatively large areain dimension when compared to solid state membrane devices, such aspiezoelectric sensors or fabricated memory chips utilizing membranes.Accordingly, the requirements from the electronics of the sensor 50 areless demanding. Additionally, the membrane 56 has a much largerdeflection than that of the solid state membrane.

The sensor 50 also includes an antenna coil 68 which is operativelyconnected to the internal components of the sensor 50 by an antenna lead70. The antenna coil 68 is an inductance coil having a spiralled coilconfiguration. The material used for the antenna wire is approximately90% silver content with a cladding of platinum iridium of approximately10% content. The antenna coil 68 is preferably made of 20-25 turns of 30μm thickness wire. The antenna outer diameter is 1.5-2.0 cm (FIG. 2).

Accordingly, due to these features, the antenna coil 68 possesses a verylow parasitic capacitance. Additionally, the antenna coil 68, due to itssilver/platinum content wire has extremely high conductivity and isextremely flexible.

Although antenna 68 is described as being external of the housing 52, itis well within the scope of the invention to include any type ofsuitable antenna, such as an antenna that is contained within thehousing 52.

The sensor 50 further includes anchoring legs 64 resiliently biased tothe exterior of the housing 52. The number of anchoring legs 64 can varydepending on the desired degree of anchoring and geography of theanatomy in which the sensor 50 is to be placed. The anchoring legs 64are made from wire utilizing shape memory metal material, such as anickel titanium alloy (NiTinol). The anchoring legs 64 have a concaveconfiguration with a radius of curvature that curves into the tissue ororgan in which the sensor 50 is to be anchored. Other appropriateconfigurations for the anchoring legs 64 are also contemplated herein.

If desireable, the sensor 50 is coated with a nonthrombogenic oranticoagulating agent such as Heparin prior to implantation in order toprevent thrombosis, clotting, etc.

FIG. 3 illustrates an alternative embodiment of the sensor 50 having atapered end 54 on the housing 52. The tapered end 54 has a tissuepiercing tip 55 and helical threads 57 arranged on an outer surface ofthe tapered end 54 in order to facilitate the direct anchoring of thetapered end 54 of the housing 52 through direct threading into tissue.

FIG. 4 illustrates another alternative embodiment sensor 50 including aplurality tissue barbs 59 fixed to the tapered end 54 of the housing 52.The barbs 59 have a tissue piercing tip curved outwardly away from thetissue piercing tip 55. Accordingly, along with the tissue piercing tip55, the tissue barbs 59 grasp firmly into the tissue for firmlyanchoring the housing 52 in the tissue.

As shown in FIG. 5, the interior of the housing 52 includes amicroprocesser 90, in the form of a microchip, fixed within one of theinterior walls of the housing 52. The lead 70 of the antenna coil 68 isoperatively connected to the microprocessor 90. Microprocessor 90includes an array 92 of photoelectric cells 95 arranged in a patternedconfiguration, e.g. eight staggered rows containing eight photoelectriccells 95 in each row. A reference photoelectric cell 97 is located atone end of the array 92 resulting in an array 92 having a total ofsixty-five photoelectric cells such as illustrated in FIG. 7. Thephotoelectric cell array 92 provides for 64 degrees of resolution. Thepitch distance between each photocell 95 is approximately ¼ the size ofa photocell 95. Additionally, the reference photocell 97 has a dimensionthat is approximately the size of the pitch, e.g. ¼ the size of aphotocell 95, thus providing a resolution that is equal to a motion of ¼of the photocell.

A light emitting diode (LED) 100 is operatively connected to themicroprocessor 90 and is positioned above and spaced parallel and awayfrom the photoelectric cell array 92. A shutter 62 is connected to theinner surface of the membrane 56 and extends longitudinally from themembrane 56 within housing 52. The shutter 62 has a substantiallyD-shaped configuration and longitudinally extends between the LED 100and the photoelectric cell array 92. The shutter 62 is made from analuminum alloy and is positioned such that the planar surface of theshutter 62 directly faces the photoelectric cell array 92. The shutter62 is fixed to the deformable membrane 56 such that the shutter 62 movesin association with the membrane 56. Accordingly, when the membrane 56is deflected inwardly into the housing 52 (due to the monitored ormeasured tissue or organ parameter), the shutter 62 longitudinallyextends over a number of photoelectric cells 95 in the array 92 indirect relation to the inward movement of the membrane 56 as it is beingdeformed. Likewise, when the membrane 56 is deflected outwardly from thehousing 52, the shutter 62 moves longitudinally outwardly from the endof the housing 52 along with the membrane 56. Accordingly, the shutter62 obscures or blocks a number of the photoelectric cells 95 inaccordance with the degree of movement of the membrane 56. Thus, whenthe shutter 62 is positioned over a specific number of photoelectriccells 95, light from the LED 100 is prevented from reaching thephotoelectric cells 95 and affects signal transmission from these cells95. This arrangement constitutes an analog-to-digital (A/D) conversionwhich is power effective since there is a simple counting of the numberof photocells that are on or off as a measure of the shutter's motion.Hence, the analog-to-digital conversion. Accordingly, the microprocessor90 operatively communicates with the membrane 56.

The reference photoelectric cell 97 is never obscured or covered by theshutter 62 since it is located at the far end (end away from themembrane 56) of the array 92. The shutter 62 and membrane 56 arecalibrated such that even upon maximum deflection inwardly into thehousing 52, it results in the reference photoelectric cell 97 beingpermanently exposed to the LED 100 for use as a reference signal for thesensor 50. Yet, the power dissipation of the photocell is very low.

As best shown in FIG. 6A, the microprocessor 90 is a circuit wherein theantenna coil 68 and a resonance capacitor 102 operate as a resonatingoscillator for the sensor 50. The antenna coil 68 receives transmittedRF signals sent by the signal reading and charging device 140 asillustrated in FIGS. 8 and 9. The RF signal received at the antenna coil68 is a charging signal for powering the microprocessor 90. Uponreceiving the RF charging signal, the antenna coil 68 and capacitor 102resonate and charge a charge capacitor 114 through diode 116. Uponreaching a predetermined voltage threshold of approximately 1.2 V, thecapacitor 114 powers the LED 100 and a logic circuit 91 through controlunit 104. Upon powering of the LED 100 by the charged capacitor 114, theLED emits light to the photoelectric cell array 92 which is kept atnegative voltage.

As illustrated in FIG. 6B, the photoelectric cell array 92 is designatedP₁, P₂, . . . P₆₄ and P_(ref), respectively. Each photoelectric cell 95(P₁-P₆₄) are connected in parallel to a plurality of comparators 120designated C1, C2 . . . C64. The reference photoelectric cell 97 isoperatively connected to each comparator 120 (C1-C64) for providing areference signal to each comparator 120 in comparison to the signalreceived from each respective photoelectric cell 95. The logic circuit91 is powered and controlled by the control unit 104 and a clock 106.The control unit 104 is connected to each comparator 120.

A buffer 126 having a plurality of buffer cells 129 (sixty-four totalbuffer cells corresponding to each comparator C1-C64) is operativelyconnected to the comparators 120. Each buffer cell 129 is a flip-flop,or memory cell, which receives a signal from its respective comparatorC1-C64 resulting in a binary number which is sixty-four digits long (aseries of ones or zeros). All buffer cells 129 are filled in a singleclock cycle and each buffer 129 has either “0” or “1” in it. After allsixty-four buffer cells 129 have been filled with its respective binarynumber, the digital signal representing all sixty-four bytes is sent tothe signal reading and charging device 140 by the control unit 104.After transmitting the digital signal, the control unit 104 is reset bythe clock 106 awaiting further signal inputs from the signal reading andcharging device 140. Encryption of the binary number is provided by thesignal reading and charging device 140 described in greater detailbelow.

Upon filling the sixty-fourth buffer cell, the digital signal istransmitted from the buffer 126 and activates switch 112 resulting in atransmission of the digital signal from the antenna coil 68 to theantenna coil 162 of the signal reading and charging device 140.

One main aspect of the system 30 of the present invention is that thesensor 50 is both a wireless transponder and a low-powered devicecapable of fast update rate, despite its passive nature, due to theinherent analog-to-digital (A/D) conversion mechanism employed in thesensor 50, e.g. the photoelectric cell array 92, which directly convertsthe membrane 56 deflection into a digital signal, with no powerconsumption as would be required for a conventional electronic A/Dconverter.

Signal Reading and Charging Device

As illustrated in FIG. 8, the signal reading and charging device 140according to the present invention is for use outside of a patient'sbody or at the exterior surface of the patient's body. The signalreading and charging device 140 includes a casing 145, which is ahousing, having a liquid crystal display (LCD) display screen 172mounted in an opening in the housing 145. The signal reading andcharging device, also commonly referred to as a read/charge device,reader/charger or reader/charger device, is activated by a power switchor toggle 146 extending from the casing 145. Antenna coil 162operatively communicates with the antenna coil 68 of the sensor 50 byinductance coupling.

As shown in FIG. 9, once the logic circuit 91 transmits the digitalsignal from the sensor 50 through sensor antenna coil 68, the couplingconstant of the reader/charger antenna coil 162 is changed and isdetected by a deep detector 168 operatively connected to thereader/charger antenna coil 162. The deep detector 168 is sensitized todetect a change in the amplitude of the signal for as low as a 0.01%change in amplitude.

A read/charge logic control unit 154 is operatively connected to thedeep detector 168 for determining the threshold for the deep detector168. The logic control unit 154 also includes a power source 151 forpowering the components of the reader/charger device 140.

The reader/charger circuit 150 further includes a processing unit 170operatively connected to the logic control unit 154. The processing unit170 contains the algorithm for converting the digital signal receivedfrom the sensor 50 (FIG. 8) into a measured parameter for the medicalparameter, condition or characteristic sensed at the implanted sensor50. Additionally, the processing unit 170 includes encryption code forencryption of the digital signal (sixty-four bit signal) usingencryption algorithms such as exclusive-OR (XOR), RSA methods (RSASecurity, Inc.), etc.

For example, where the parameter being measured is hemodynamic bloodpressure, within an organ such as the chamber of a heart, once theprocessing unit 170 receives the digital signal, the processing unit170, through its algorithm, converts the digital signal (binary number)to a pressure value, using a look-up comparison table, or analyticalexpression representing the relation between the shutter 62 deflectionin the sensor 50 versus the exterior sensor pressure at the membrane 56,which is given below:

P=(KD ³ /A ²)X ²

where P is the pressure value, D is the thickness of the membrane, A isthe membrane radius, X is the deflection from the equilibrium and K is aconstant.

The LCD display 172 is operatively connected to the processing unit 170for displaying the measured parameter (hemodynamic blood pressure in theexample above) converted from the digital signal in real time.

By utilizing the signal reading and charging device 140 at the exteriorof the patient's body, continuous parameter readings (for determiningaspects of the parameter such as magnitude) are obtainable for both themean and active or individual values of the sampled parameter.

When measuring characteristics of a body fluid such as blood, the signalreading and charging device 140 maintains an active reading volumearound the sensor 50, ranging anywhere from 5-25 cm, and preferably, anactive reading volume ranging approximately 10-15 cm. Moreover, with thetelemetric medical system 30, through the sensor 50, and the signalreading and charging device 140, it is possible to sample multiplereadings per second. Preferably, approximately 10-20 readings per secondare possible with the present invention.

Other attributes associated with the present invention when utilized asa pressure monitor in a chamber of the heart include monitoring apressure range of +/−30 mmHg; an accuracy (at 5 mSec. integration) of+/−1 mmHg with a repeatability (at 5 mSec. integration) of +/−1 mmHg. Itis important to note that the pressure boundaries can be changed easilyby changing the size and dimensions, such as width, of the membranewithout any change to the electronics. This is important for allowingthe present invention to be adapted for various applications while usingthe same design.

The control unit 154 is also operatively connected to a sine-wave driver158 for generating a sinusoidal wave signal of approximately 4 to 6 MHz.The sinusoidal wave signal is generated by the sine-wave driver 158through capacitor 160 to the reader/charger antenna coil 162 fortransmission or sending to the antenna coil 68 of the sensor 50 in orderto power or charge the sensor 50 as described above.

Medical Procedures

As mentioned above, the telemetric medical system 30 according to thepresent invention is useful for nearly any type of medical diagnosticprocedure where it is desireable to implant the sensor 50 at a portionof the body, particularly tissue or organ of interest. The telemetricmedical system 30 according to the present invention allows for remotemonitoring and diagnosis of a condition of the tissue or organ by beingable to rapidly sample various parameters or variables of any physicalcondition within the patient's body at the site of interest. Since thetelemetric medical system 30 is wireless, these types of procedures areconducted in a completely non-invasive manner with minimal trauma to thepatient.

One particular example for the telemetric medical system 30 according tothe present invention, its components and their method of use, is in thefield of congestive heart failure (CHF). CHF is defined as a conditionin which a heart 400 (FIG. 10) fails to pump enough blood to the body'sother organs. This can result from narrowed arteries that supply bloodto the heart muscle (due to coronary artery disease), past heart attack,or myocardial infarction, with scar tissue that interferes with theheart muscle's normal work, high blood pressure, heart valve disease dueto past rheumatic fever (in valves such as semilunar valve, tricuspidvalve 417 or mitral valve 418) or other causes, primary disease of theheart muscle itself, called cardiomyopathy, defects in the heart presentat birth such as congenital heart disease, infection of the heart valvesand/or heart muscle itself (endocarditis and/or myocarditis).

The ailing heart 400 keeps functioning but not as efficiently as itshould. People with CHF cannot exert themselves because they becomeshort of breath and tired. As blood flowing out of the heart 400 slows,blood returning to the heart 400 through the veins backs up, causingcongestion in the tissues. Often swelling (edema) results, most commonlyin the legs and ankles, but possibly in other parts of the body as well.Sometimes fluid collects in the lungs and interferes with breathing,causing shortness of breath, especially when a person is lying down.Heart failure also affects the ability of the kidneys to dispose ofsodium and water. The retained water increases the edema.

CHF is the most common heart disease in the United States and it isestimated that over 5 million patients suffer from it. One of the morepredictive hemodynamic parameters being measured in patients with CHF isblood pressure in the left atrium 410, e.g. left atrial (LA) pressure.To date, this parameter is measured by employing invasive right heartcatheterization with a special balloon catheter such as the Swan-Gantzcatheter.

Accordingly, in moderating for effects of CHF, it is desireable tomeasure the blood pressure in a particular chamber (either right atrium415, right ventricle 419, left atrium 410 or left ventricle 420) in theheart 400 utilizing the telemetric medical system 30 according to thepresent invention.

Accordingly, in conducting one preferred method according the presentinvention, blood pressure can be directly monitored in the left atrium410 of the heart 400. Accordingly, it is desireable to implant thesensor 50 at fossa ovalis 407 within the septum 405.

With respect to the specific anatomy of the septum 405, in approximately15% of the normal population, the fossa ovalis 407 has a pre-existinghole or opening that either remains open or patent and is normallycovered by a small flap of tissue. In approximately 85% of the normalpopulation, the fossa ovalis 407 is completely occluded, e.g. there isno hole in the septum 405.

(1) Transcatheter Approach

In accordance with the method according to the present invention, atranscatheter approach has been found to be particularly useful for thepatient population already having the pre-existing hole at the fossaovalis 407. Accordingly, in performing this method according to thepresent invention, first, a transesophageal ultrasonic probe (not shown)is inserted into the patient's mouth and placed in the esophagus. Inmost cases, the transesophageal ultrasonic probe is positionedapproximately 30-35 cm from the mouth, i.e. in most cases positionedjust above the patient's stomach.

Under transesophageal ultrasonic guidance, a wire (not shown) isinserted into the right atrium 415 through an appropriate vessel such asthe inferior vena cava 408 wherein the wire is guided through the fossaovalis 407 by gently lifting the tissue flap away from the patentopening at the fossa ovalis 407. Once the wire is inserted through thefossa ovalis 407, the wire is guided to one of the pulmonary veins 416for placement of the distal end of the wire in order to properlyposition and anchor the wire in the opening of the pulmonary vein 416.Accordingly, the pulmonary vein 416 has been proven to be a veryreliable and steady anchoring point for the wire.

Once the wire is properly positioned in the fossa ovalis 407 andanchored in the pulmonary vein 416, a catheter sheath (“over-the-wire”type—not shown) is guided over the wire through the right atrium 415 andthe fossa ovalis 407 and positioned within the left atrium 410, forinstance, very close to the opening of the pulmonary vein 416.

Once the catheter sheath has been properly positioned, the wire isremoved from the patient's heart 400 and the sensor 50 is deliveredthrough the catheter sheath by one of the many standard catheter-baseddelivery devices (not shown). Accordingly, the sensor 50 can bedelivered to the fossa ovalis 407 by any of the typical catheter-baseddelivery devices normally associated with implantable pacemakers,electrodes, atrial septal defect (ASD) occlusion devices, etc.Accordingly, the sensor 50 is deliverable with typical delivery devicessuch as the Amplatzer® Delivery System, manufactured by AGA MedicalCorporation of Golden Valley, Minn.

After placement of the catheter sheath, the sensor 50 is deployed fromthe catheter sheath within the fossa ovalis 407 as best illustrated inFIG. 11. Upon deployment, the sensor 50 utilizes the anchoring legs 64for anchoring the sensor 50 to the septum 405 and occluding the openingat the fossa ovalis 407.

(2) Anterograde Approach

The sensor 50 is placed in the fossa ovalis 407 for those patients nothaving a pre-existing opening in the fossa ovalis 407 through means ofan anterograde approach. Once again, a transesophageal ultrasonic probeis positioned in the patient's esophagus as described above. Undertransesophageal ultrasonic imaging guidance, an opening is made in theseptum 405 at the fossa ovalis 407 in order to place and accommodate thesensor 50. Thus, the opening is made with a standard needle catheter(not shown) such as the BRK™ Series Transseptal Needle manufactured bySt. Jude Medical, Inc. of St. Paul, Minn. Accordingly, undertransesophageal ultrasonic guidance, the needle catheter is initiallyplaced in the right atrium 415 and positioned at the fossa ovalis 407.At this point, the tip of the needle of the needle catheter penetratesthe fossa ovalis 407 and the catheter is inserted through the fossaovalis 407 into the left atrium 410 through the newly created opening inthe fossa ovalis 407 by the needle catheter. Once the opening in thefossa ovalis 407 is created, the sensor 50 is introduced with thedelivery device, such as the delivery device described above, and placedin the fossa ovalis opening as shown in FIG. 11. Upon deployment of theanchoring legs 64, the opening in the fossa ovalis 407 is occludedaround the sensor housing 52 and the sensor 50 fixed to the septum 405in a secure fashion.

It is important to note that transesophageal ultrasonic imaging isutilized for both the transcatheter and the anterograde approach asdescribed above in accordance with each method step of the presentinvention. Since either method according to the present invention can beutilized with the transesophageal ultrasonic guidance, other imagingmodalities such as flouroscopy can be eliminated. As such, the methodsaccording to the present invention can be conducted in an outpatientclinic or doctor's office as a bedside procedure. By eliminating theneed for a flouroscope, the method according to the present inventionalso eliminates the need for conducting the procedure in a catheter labwhich only adds additional time and cost to the procedure and additionaltime and inconvenience to the patient.

After the sensor 50 has been implanted in the patient's septum 405, thepatient is provided with standard treatment to prevent excessivecoagulation or endothelialization. For instance, it is common practiceto prescribe aspirin and/or an anticoagulant such as Heparin for aperiod of time such as six months.

With either of the methods described above, the sensor 50 is fixed tothe septum 405 in order to provide real time pressure monitoring in theleft atrium 410. Since the sensor 50 is a wireless transponder and abattery low power receiver, the sensor 50 does not impede the naturalfunction of the heart 400 and is truly minimally invasive.

By utilizing the signal reading and charging device 140 at the exteriorof the patient's body, continuous pressure readings are obtainable forboth the mean and pulsating values of pressure in the left atrium 410provided by the sensor 50.

With the telemetric system 30, the signal reading and charging device140 maintains an active reading volume around the sensor 50 ranginganywhere from 5-25 cm, and preferably, an active reading volume rangingapproximately 10-15 cm. Moreover, with the sensor 50, and the signalreading and charging device 140, it is possible to sample multiplereadings per second. Preferably, approximately 10-20 readings per secondare possible with the present invention.

Other attributes associated with the present invention when utilized asa pressure monitor in a chamber of the heart include monitoring apressure range of plus/minus 30 mmHg; and accuracy (at five Mmsec.integration) of plus/minus 1 mmHg and a repeatability (at 5 msec.integration) of plus/minus 1 mmHg.

Although preferred embodiments are described hereinabove with referenceto a medical system, devices, components and methods of use, it will beunderstood that the principles of the present invention may be used inother types of objects as well. The preferred embodiments are cited byway of example, and the full scope of the invention is limited only bythe claims.

What is claimed is:
 1. A telemetric medical system comprising: atelemetric medical sensor for implantation in a patient's body formeasuring a parameter therein, the sensor comprising a housing, amembrane at one end of the housing, the membrane being deformable inresponse to the parameter, and a microchip positioned within the housingand operatively communicating with the membrane for transmitting asignal indicative of the parameter; and a signal reading and chargingdevice locatable outside of a patient's body for communication with thesensor, the signal reading and charging device comprising a casing; anda circuit within the casing, the circuit comprising a logic control unitand a processing unit, the logic control unit for sending a poweringsignal to the sensor for remotely powering the sensor, the logic controlunit also for receiving the transmitted signal from the sensor, theprocessing unit operatively connected to the control unit for convertingthe transmitted signal by the sensor into a measured parameter.
 2. Thesystem of claim 1, wherein the signal transmitted by the sensor is adigital signal.
 3. The system of claim 2, wherein the sensor furthercomprises an antenna operatively connected to the microchip.
 4. Thesystem of claim 3, wherein the antenna is located at the exterior of thehousing.
 5. The system of claim 2, wherein the signal reading andcharging device includes an antenna coil for sending the powering signalto the sensor and for receiving the transmitted digital signal from thesensor. 6.The system of claim 5, wherein the signal reading and chargingdevice includes a display for displaying the measured parameter.
 7. Thesystem of claim 6, wherein the display is an LCD screen.
 8. The systemof claim 6, wherein the signal reading and charging device includes asine wave driver operatively connected to the control unit for sendingthe powering signal to the sensor.
 9. The system of claim 8, wherein thepowering signal is a sinusoidal wave signal approximately 4-6 MHz. 10.The system of claim 5, wherein the processing unit decodes thetransmitted signal.
 11. The system of claim 10, wherein the signalreading and charging device includes a deep detector for receiving thetransmitted signal.
 12. The system of claim 11, wherein the signalreading and charging device includes a power source operativelyconnected to the circuit.
 13. The system of claim 12, wherein the signalreading and charging device includes a power switch for activating anddeactivating the device.
 14. The system of claim 2, wherein themicrochip comprises an array of photoelectric cells.
 15. The system ofclaim 14, further comprising an LED for transmitting light at thephotoelectric cells.
 16. The system of claim 15, wherein the sensorfurther comprises a shutter connected to the membrane and moveablebetween the photoelectric cells and the LED in response to deforming ofthe membrane.
 17. The system of claim 16, wherein the photoelectriccells are arranged in staggered rows.
 18. The system of claim 17,wherein the array includes a reference photoelectric cell.
 19. Thesystem of claim 19, wherein the reference photoelectric cell is notblocked by the shutter.
 20. The system of claim 19, wherein themicrochip further comprises a plurality of comparators operativelyconnected to the photoelectric cells.
 21. The system of claim 20,wherein the microchip further comprises a buffer operatively connectedto the comparators for storing and transmitting the digital signal. 22.A method for telemetrically measuring a parameter in a patient's bodycomprising the steps of: providing a telemetric medical sensorcomprising a housing, a membrane at one end of the housing, the membranebeing deformable in response to the parameter, and a microchippositioned within the housing and operatively communicating with themembrane for transmitting a signal indicative of the parameter;implanting the sensor at a site within the patient's body; andtelemetrically measuring the parameter from outside of the patient'sbody.
 23. The method according to claim 22, including telemetricallypowering the sensor from outside of the patient's body.
 24. The methodaccording to claim 23, including telemetrically measuring the parameterand telemetrically powering the sensor from outside the patient's bodywith a signal reading and charging device comprising a casing, and acircuit within the casing comprising a log control unit and a processingunit, the logic control unit for sending a powering signal to thetelemetric medical sensor for remotely powering the sensor, the logiccontrol unit also for receiving the transmitted signal from the sensor,the processing unit operatively connected to the control unit forconverting the transmitted signal by the sensor into the measuredparameter.
 25. The method of claim 24, including displaying the measuredparameter.